SEARCH=INTHREAD not announced in capabilities

[kael]

Hello,

Looking at the SEARCH=INTHREAD extension, Dovecot implements it but the 
server doesn't announce the extension in its capabilities (at least 
testing with imap://dovecot.org or looking at 
https://github.com/dovecot/core/blob/169b1ff42a28cdf2768391d20e8fef13aeae54fb/configure.ac#L783 
)

It does work though:

a UID SEARCH INTHREAD REFS HEADER subject "Re: bash script"
* SEARCH 106075 106076 106084
a OK Search completed (1.047 + 0.000 + 1.046 secs).

I'd have thought that announcing THREAD=REFS would imply 
SEARCH=INTHREAD, but testing with Fastmail only the former is implemented.

Looks like a bug in Dovecot as the client can't discover the 
SEARCH=INTHREAD capability.

Cheers.

-- 
kael